Process for producing magnetic sheet materials



developing a double oriented magnetic structure.

alloy during the final annealingztreatment;

United States Patent ."This invention relates to an improved annealing process for obtaining double oriented orrcube textured iron-silicon magnetic alloy sheets.

For a better understanding of therinvention reference I may be had to copending application Serial No. 85,432, filed January- 27, 1961, now abandoned, and to the continuation-in-part thereof, application Serial No. 154,803, filed November 24, 1961, entitled, Cube Textured lron- Silicon 'Magnetic Alloy Sheets and Process for Making the Same, by G. W. Wierner et al., assigned to the assignee of the present application, wherein there is disclosed a novel iron-silicon alloy, particularly suitable for It is to they annealing treatment of alloys of the type described pending applications are that certain minimum amounts of sulfur must be present in the alloy sheets if the trans formation to cube grain texture is to go to completion in the final annealing treatment.

As explained in detail in the copendmg application, the.

final annealing treatment is carried out in an atmosphere of very dry hydrogenor in vacuum; -Under these conice * in the final annealing treatment of iron-silicon base alloy sheets to promote transformation of a high volume of the sheets to cube grain texture.

More particularly, the sulfunbearing A1 0 powder consists essentially of at least 0.001% sulfur, by Weight, and the balance A1 0 except for small amounts of incidental impurities. Oxygen and readily decomposible oxides, such as water, carbonates and hydroxides should not be present inthe alumina. A preferred range of sulfur content within the broad range stated above is from 0.005% to 0.02% by weight of sulfur.

The process for making sulfur-bearing A1 0 powder involves placing a quantity of the A1 0 in'a furnace, heating the powder to a temperature in the' range from 800 C. to l300 C. for from 2 to25 hours in a hydrogen atmosphere containing from 5 to 500 parts per million of H 8. The temperatures of the heat treatment will drive off any water. The heat treated powder may then be stored in sealed containers until needed.

The method for the final anneal of stacked or coiled iron-silicon alloy sheet involves providing a thin separating layer of the sulfur bearing A1 0 in an amount of of sheet, between each sheet'of the stack or between adjacent turns of the coil, annealing thealloy sheet ata temperaturefrom about 1100 C. to 1350 C. to

affect substantially complete secondary recrystallization in an atmosphere capable of reducing or causing the disappearance of surface oxide/films. The atmosphere of the final anneal may be a very dry hydrogen having, for example, from 40 to 70 C. dew point or lower or a high vacuum of less than 10 microns.

ditions, the sulfur present in the alloy sheets which is 1 necessary for successful transformation to cube texture,

effort of this invention is directed to preventing such undesirable loss of sulfur from the sheets of iron-silicon In commercial practice the final annealing is of sulfur adjacentthe iron-siliconsheets to which it is It is an ob ect of this invention to provide in. the final annealing treatment" of stacked or coiled iron-silicon alloy vsheets a method for introducing sulfur into the area. immediately adjacent the surfaces 7 of the alloy sheet which comprises providing a thin layer of a sulfurbearing A1 0 as the separating medium between sheets.

,It is...another object of this invention to provide a method for producing sulfur-bearing A1 0 which com prises exposing A1 0 powder to a hydrogen atmosphere containing a small amount of l-l sftherein at an elevated temperature.

Still another object of the invention is to provide an A1 0 powder containing a small-but critical'amountof i sulfur therein. r

Other objects of this invention; will, in pargbe ob i I and will,,inpart, appear herein f a This invention is directed to' a. sulfur-bearing powder which can supply sulfunto the surrounding .en-

vironment at elevated temperature, to a methodfor preparing this sulfur-bearing A1 0 powder, and to it carried out on sheet assemblies either in'stacked form or in As a demonstration of the advantages of the use of thesulfur-bearing A1 0 powder of this invention, final anneals were carried out on a heat identified as Number 8023, of which the following is a typical analysis of cold rolled sheets of final gauge:

Per- Per- Per- Per- Per- Per- Percent Si cent 0 cent N cent S cent 0 cent P cent Al 2. 98 .003 .002 .001 001 003 The balance of the alloy was, of course, iron except for small amounts of incidental impurities. Material of the above analysis had been arc melted cold rolled to .012 inch thick sheet and punched into laminations.

The sheet material in this stage of the process had a rather poor surface finish Which would normally be expected to impede cube grain growth. Therefore, some of the laminations were polished with a mixture of.

- '(A) 24 unpolished laminations and 12 polished laminations .of the iron-silicon alloy were stacked between high temperature alloy plates of nickel-base alloy known 'as lnconel with 'pure A1 0 powderlinterposed to separate the laminations and preventsticking. The stack of laminations were heated in a tube furnace for 40 hours at' 1200 C; in dry hydrogen having a dew point of -60 C.

(B) 45 polished and 45 unpolished laminations were stacked between plates of nickel-base alloy, usingsulfunbearing A1 0 powder as a separating medium. The 'Al O powder had previously been heat treated for 16,

'hourszat 1200 C. in a dry hydrogen atmosphere con method for employing the sulfur-bearing A1 0 powder,

taining between 50 and 200 parts per million oil- S gas.

The stack of laminations washeat treated for 26 hours at- 1200 C. in dry hydrogen having a dew point of sulfur content by this test.

In the tests, the alloy sheets to be treated by the process of the invention were clean and flat pn'or to heat treat-,

used to apply a thin uniform layer of powder of from 1 to 10 grams per square foot of surface area between the sheets. Amounts greater than 10 grams per square foot of surface are not necessarily detrimental. The stack was loaded uniformly so that there were no visible large spaces between the sheets. The loading was accomplished by tightening bolts which passed through the top and bottom nickel-base alloy plates. Each stack of laminations was. packed in A1 powder and. surrounded with nickel-base alloy (lnconel) plates to cut down the flow of gas against the laminations. The stack of laminations was heated at 1200 C. in the dry hydrogen for a time sufficient to provide complete secondary recrystallization and maximum attainable cube grain growth, usually be the lamination must be cube-on-face grains. The following results were obtained:

Table 1 Average volume Percent acceptable Percent Transformed I Heat Treatment The results indicate the great improvement obtainable' by using the sulfur-bearing A1 0 powder as a sheet separator in the final anneal. It is to be particularly noted that when the sulfur-bearing powder was employed,

Unpolished Polished Unpolished Polished 60' s0 20 70 95 100 r 100 t 100 p decomposition noted in the previous table.

- i- 7 (70 C. dew point) for 16 hours. When the A1 0 powder after the anneal was analyzed it contained 0.002% by weight of sulfur. Thus, it is demonstrable that during a final anneal of the type described sulfur is evolved from thfi A1203. 7

It is interesting to .note that the sulfur content of the Al O powder deteriorates with time at room temperature in air. A sample showed the following characteristics with time.

Table II Days after treatment: Percent S O .012

While some experimental fluctuations will be noted in the above data, it is clear that the sulfur content marked- 1y declines over the test period.

It has also been observed that having the treated A1 0 open to relatively fr'ee circulation of air accelerates the The following results were obtained on another sample in which a part was kept in a sealed container and a partin a similar container with the cover open.

Table III Days on Percent test S Sample closed Sample closed Sample open i is retained after cooling. During the final anneal treatthe cube texture secondary recrystallization grain growth 7 in the iron-silicon alloy sheets is much less sensitive to surface conditions of the sheets. i

In preparing the sulfur-bearing A1 0 powder a shallow layer of powder of from 80 to 150 mesh fineness, is placed in a nickel-base alloy boat in a furnace. The powder is heated to a temperature in the range from 809 C. to 1300 C., and preferably about 1200 C., for from 2 to 25 hours in a hydrogen atmosphere containing from 5 toSOO parts per million of hydrogen sulfide. Thus, in one successful process, hydrogen gas containing a concentration of H 5 of about-5 parts per million, flowing the addition of HCl to ensure-the dissolution of all the sulfur in the powder.

The solution is then titrated with a .01 N K10 solution. The total weight of sulfur in the A1 0 powder can then be calculated, and the sulfur is reported as a weight percentage of the A1 0 powder.

A sample that had not been treated with H 8 showed no A sample that had been treated for 16 hours in hydrogen containing 5 parts per million H 8 analyzed .009% by weight of sulfur. This sample was then used as the separating medium in a final anneal for transforming iron-silicon alloy sheets to cube texture at atemperature of 1200 C. in pure hydrogen ment which has been described, the A1 8 reacts with hydrogen gas to form H 8 at the surface of the ironsilicon alloy sheets, which hydrogen sulfide at the sheet surface aids the cube growth process. It is known that A1 8 decomposes in moist air to form H 5. Thus, it appears that air must be excluded from the treated Al O powder if it is to be stored for any length of time.

While applicant has advanced a proposed explanation for the phenomena observed he does not wish to be bound thereby, for other unknown factors-may be at work in the process. The prime requirement is that sulfur is chemically associated with the A1 0 powderin such a way that it is available for the final annealing process. Where the term sulfur-bearing Al O is employed in this application, it'will be understood to mean that the sulfur is chemically associated with the aluminum or alumina. I

Table-lV Volume Typical Wt., Percent Percent S Cube Grains Run Treatment otAl Oa N0.

005 to 02 95 .-001.t0 .002 OOI'tO .002 77 :001 61 H OOCJDOLPOO A series of final annealing treatments was made on a typical 3% silicon-iron alloy, identified as heat No. 1263. The typical analysis of this alloy is similar to heat No. 8023 set forth above with the difference that while 8023 had essentially no manganese, heat No. 1263 contains about 0.2% manganese. Table IV above shows data giving the amount of cube growth obtained in heat No. 1263 alloy sheets for different treatments of A1 0 The final annealing treatment used was 16 hours at 1200 C. in pure dry hydrogen (70 C. dew point) and all annealing factors were kept constant. Run 1 was done with pure untreated A1 0 powder and shows that with a standard final annealing treatment only 54% cube grain growth took place in this alloy. Run 2 was made to show 7 that high temperature purification of the A1 0 was not a factor, and it is clear that this had essentially no effect since the cube growth is approximately the same as 1n run 1.

The above tests show that the A1 0 powdershould contain between .005 and .02% sulfur, by weight, w

fugitive nature of sulfur under the conditions of a vacuum ture;

anneal, maintaining a desired sulfur concentration in the steel has been most difficult, 'with the result that cube texture transformation results have not been consistent. The use of sulfur-bearing A1 0 powder in vacuum annealing processes to obtain cube texture grain growth in iron-silicon 'alloy sheets has been as highly successful in vacuum annealing as it has been shown to be in hydrogen annealing,

The effect of sulfur-bearing A1 0 in vacuum annealing was demonstrated with a .008 inch thick sample of 3% silicon-iron, with essentially the same or similar alloy composition as those given above. In a standard vacuum anneal employing a vacuum of about .01 micron and using pure A1 0 for separating the sheets, only about 50% transformation to cube texture was obtained. For an identical anneal using sulfur-bearing A1 0 powder of the type described herein which contained about 0.007% sulfur, 100% transformation to cube texture was obtained in the same alloy sheet. I

There has thus been described a relatively simple means for supplying sulfur to the atmosphere immediately adjacent the surface" of iron-silicon alloy sheets undergoing I final annealing treatmentfor transformation to cube tex- The sulfur-bearing A1 0 powder employed is easily, made and readily employed in final annealing PIOCGSSES.

It is to be understood that all matter described herein is to be interpreted, as illustrative and not as a limitation.

sheet, the method for introducing sulfur into the area immediately adjacent the surface of the alloy sheet in an amount sufiicient to promote cube texture grain growth comprising, providing a thin separator layer of sulfurbearing A1 0 containing at least 0.001% by weight of sulfur on the surface of the alloy sheet, and annealing the alloy sheet in contact with said separator layer at a temperature of from 1100 C. to 1350 C. in an atmosphere capable of causing the removal of surface oxide films, for a period of time to cause substantially complete secondary recrystallization.

2. The method of claim 1 in which the atmosphere consists essentially of dry hydrogen having a dew point of at least 40 C. 1

3. The method of claim 1 in which the atmosphere is a vacuum of at least about 0.01 micron.

4. In a final annealing treatment for stack-ed or coiled iron-silicon alloy sheet, the method for introducing sulfur into the area immediately adjacent the surface of the alloy sheet in an amount sufiicient to promote cube texture grain growth comprising providing a thin separator layer of A1 0 powder containing from 0.005% to .02% sulfur, by weight, on the surface of the alloy sheet, andannealing the alloy sheet at a temperature of from 1100 C. to 1350 C. in contact with said separator layer in an atmosphere capable of causing the removal of surface oxide films, for a period of time to cause substantially complete secondary recrystallization.

5. The method of claim 4 in which the atmosphere consists essentially of dry hydrogen having a dew point of at least 40 C. g

6. The method of claim 4 in which the atmosphere is a vacuum of at least about .01 micron.

7. In a method for treating an assembly or iron-silicon alloy sheet material in coil or sheet form to obtain a high volume proportion of cube grains the steps comprising, finally annealing the assembly in a highly reducing atmosphere at a temperature of from 1100" C. to 1350 C. in contact with sulfur-bearing A1 0 containing at least 0.001% sulfur as the result of exposure to a hydrogen atmosphere containing from 5 to 500 parts per million of H 8 at an elevated temperature.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Journal of Applied Physics, supplement to vol. 31, No. 5, May 1960 (pages 4088-4095 relied upon). 

1. IN A FINAL ANNEALING TREATMENT FOR IRON-SLILICON ALLOY SHEET, THE METHOD FOR INTRODUCING SULFUR INTO THE AREA IMMEDIATELY ADJACENT THE SURFACE OF THE ALLOY SHEET IN AN AMOUNT SUFFICIENT TO PROMOTE CUBE TEXTURE GRAIN GROWTH COMPRISING, PROVIDING A THIN SEPARATOR LAYER OF SULFURBEARING AL2O3 CONTAINING AT LEAST 0.001% BY WEIGHT OF SULFUR ON THE SURFACE OF THE ALLOY SHEET, AND ANNELAING THE ALLOY SHEET IN CONTACT WITH SAID SEPARATOR LAYER AT A TEMPERATURE OF FROM 1100*C. TO 1350*C. IN AN ATMOSPHERE CAPABLE OF CAUSING THE REMOVAL OF SURFACE OXIDE FILMS, FOR A PERIOD OF TIME TO CAUSE SUBSTANTIALLY COMPLETE SECONDARY RECRYSTALLIZATION. 